THE BUILDING OF A BIRD
It rained on Wednesday--a warm spring rain, swelling the rivers and
ponds, and watering the newly planted garden; but discouraging the birds
in their nest-building, and disappointing Nat and Dodo, who wished to
have their lesson in the orchard.
"Come in here, children," said the Doctor. "The wonder room, as Dodo
calls it, is a good place for a talk about feathers and bones, and the
rest of the things birds are built of. I have sent for Rap, too, so that
the trio may be complete."
"Feathers and bones for building birds?" said Nat. "What a queer idea
for a bird story."
"Not a bird story exactly," answered the Doctor. "But some things are
true of all birds, and you must know them if you wish to understand the
_reason why_ of any bird in particular."
In a few minutes the three children were seated on the wide settle, with
a cheery log fire, to make them forget the outside dampness. Quick, the
fidgety little fox-terrier, sat by the hearth, watching a possible mouse
hole; and Mr. Wolf, the tawny St. Bernard, chose the rug as a
comfortable place for finishing his morning toilet.
Olive presently joined the group. The Doctor took the dead
White-throated Sparrow from the table, and began to walk about the room,
stopping now in front of the fire and then by the window.
"Here is a Sparrow, different from every other kind of Sparrow,
different indeed from any other sort of bird in the world--else it would
not be the particular sort of a Sparrow called the White-throated. But
there are a good many things that it has in common with all other birds.
Can you tell me some of them?"
"I know!" said Dodo; "it has a good many feathers on it, and I guess all
kinds of birds wear feathers, except some when they are very little in
the nest."
"Quite right, little girl," said the Doctor. "Every bird has feathers,
and no other animal has feathers. So we say, 'A bird is known by its
feathers.' But what do you suppose its feathers are for?"
"To make it look nice and pretty," said Dodo promptly.
"To make it lighter, so's it can fly," added Nat.
"To keep it warm, too, I guess," was Rap's answer.
"Well, you are all three partly, but not quite, right. Certainly the
beauty of a bird depends most on its feathers, being not even skin-deep,
as you may well believe, if you ever noticed a chicken Mammy Bun had
plucked. But, Nat, how can feathers make a bird lighter, when every one
of them weighs something, and a bird has to carry them all? They make a
bird a little heavier than it would be without them. Yet it is quite
true that no bird could fly if you clipped its wings. So some of its
feathers enable it to fly--the large ones, that grow on the wings. Then,
too, the large ones that make the tail help the bird to fly, by acting
like a rudder to steer with. Perhaps the small ones too, all over the
body, are of some help in flight, because they make a bird smooth, so
that it can cut through the air more easily--you know they all lie one
way, pointing backward from their roots to their tips. Then when Rap
said feathers keep a bird warm, he guessed right. Birds wear plumage as
you do clothes, and for the same purpose--to look nice and keep warm."
"But what is 'plumage,' Uncle Roy?" asked Dodo; "I thought you were
talking about feathers."
"So I was, missy. Feathers are the plumage, when you take them all
together. But see here," added the Doctor, as he spread the Sparrow's
wings out, and held them where the children could look closely; "are the
wings all plumage, or is there something else?"
"Of course there's something else to wings," said Dodo; "meat and bones,
because I've eaten chickens' wings."
"Why didn't you say, Dodo, because there has to be something for the
feathers to stick into?" said Nat decidedly.
"You both have very good reasons," said the Doctor. "The plumage of the
wings grows out from the skin, just as feathers grow from any other part
of the body, only the large ones are fastened to the bones, so that they
stay tight in their proper places. If they were loose, they would fly up
when the bird beats the air with its wings, and get out of order. See
how smoothly they lie one over another! When the bird closes its wings,
they come together snugly along its sides. But when the wing is spread,
they slide apart--yet not too far to form a broad, flat surface, quite
stiff, but light and elastic. By beating the air with the wings birds
fly along. It is something like rowing a boat. This surface pushes
against the air as the flat blade of an oar pushes against the water.
That is why these large stiff feathers are called the rowers. When the
Wise Men talk Latin among themselves, they say _remiges_, for 'remiges'
means rowers."
"But, Doctor," said Rap, who was looking sharply at the Sparrow's wing,
"all the feathers are not like that. Here are a lot of little ones, in
rows on top of the wing in front, and more like them underneath,
covering over the roots of the rowing feathers. Have they any name?"
"Oh, yes! Everything you can see about a bird has its own name. Those
small feathers are called _coverts_, because they cover over the roots
of the rowers. Those on top are the upper coverts; those underneath are
the under coverts, or lining of the wings. Now notice those two pretty
bands of color across the Sparrow's wing. You see one band is formed by
the tips of the longest coverts, and the other band by the tips of the
next longest coverts. Those two rows of feathers are the greater and
middle coverts, and all the smallest feathers, next to the front edge of
the wing, are called lesser coverts. Now look at the tail, Rap, and tell
me what you can find."
"Why, there is a bunch of long stiff feathers like rowers, that slide
over each other when you spread the tail, and a lot of short feathers
that hide the roots of the long ones. Are they rowers and coverts too?"
"A bird does not row with his tail--he steers with it, as if it were a
rudder; and the long feathers are therefore called rudder-feathers--or
_rectrices_, which is Latin for rudders. But the short ones are called
coverts, like those of the wings--upper tail-coverts, and under
tail-coverts."
"How funny!" said Dodo, "for a bird to have to row himself and steer
himself all at once. I know I should get mixed up if I tried it with a
boat. How do feathers grow, Uncle Roy?"
"Just like your hair, little girl," said the Doctor, patting her on the
head, "or your nails. Didn't you ever notice the dots all over the skin
of a chicken? Each dot is a little hole in the skin where a feather
sprouts. It grows in a sheath that pushes out of the hole, like a plant
coming up out of the ground from its root. For a while this sheath is
full of blood to nourish the growing feather; that is why new feathers
look dark and feel soft--pin-feathers they are called. The blood dries
up when the feather has unfolded to its full size, leaving it light and
dry, with a horny part at the root that sticks in the hole where it
grew, and a spray-like part that makes up most of the feather. The horny
part becomes hollow or contains only a little dry pith; when it is large
enough, as in the case of a rowing feather from a Goose's wing, it makes
a quill pen to write with. But the very tiniest feather on this Sparrow
is built up in the same way.
"See! here is one," continued the Doctor, as he twitched out a feather
from the Sparrow's back. "You see the quill part runs in the middle from
one end to the other; this is called the _shaft_. On each side of it
all along, except just at the root, the spray-like parts grow. They are
called the _webs_ or _vanes_. Now look through this magnifying glass at
the web."
The children looked in turn, and each, exclaimed in wonder at the sight.
"Yes, it is very wonderful. The web, that looks so smooth to the naked
eye, is made up of a great many small shafts, called _barbs_, that grow
out of the main shaft in rows. Every one of these small side-shafts has
its own rows of still smaller shafts; and these again have little
fringes along their edges, quite curly or like tiny hooks, that catch
hold of the next row and hold fast. So the whole feather keeps its
shape, though it seems so frail and delicate."
"Are all feathers like this one?" asked Rap.
"All are equally wonderful, and equally beautiful in construction; but
there is a good deal of difference in the way the webs hold together.
Almost all feathers that come to the surface are smooth and firm, and
there is not much difference except in size, or shape, or color. For
example, the largest wing-feather or tail-feather of this Sparrow is
quite like the one I pulled out of its back in texture, only the
back-feather is smaller and not so stiff. But near the roots of these
feathers you notice a fluffy part, where the webs do not hold together
firmly. Some feathers are as fluffy as that in their whole length. Such
are called down-feathers, because they are so downy. Birds that run
about as soon as they are hatched are always clothed in down, like
little chickens, before their other feathers sprout; and some birds,
like Ducks, wear a warm underclothing of down their whole lives. Then
again some feathers do not have any webs at all--only a slender shaft,
as fine as a hair."
"Do feathers keep on growing all the time, like my hair?" asked Dodo.
"No, my dear. They stop growing as soon as they are of the right size;
and you will find your hair will do the same, when it is long
enough--though that won't be for a good many years yet, little girl.
When the blood that has fed the growing feather is all dried up, the
feather ceases to grow. Then after a while longer, when it has become
ragged and worn, it gets loose in the skin and drops out--as I am sorry
to say some of my hair is doing already. That is what we call
_moulting_."
"I know about that," interrupted Nat. "It's when hens shed their
feathers. But I didn't know that it was moulting when people grow bald."
"It is very much the same thing," said the Doctor, "only we don't call
it moulting when people lose their hair. But there is this difference.
Birds wear out their feathers much faster than we do our hair, and need
a new suit at least once a year, sometimes oftener. All young birds get
their first new clothes when the down is worn out. Old birds generally
moult as soon as they have reared their broods, which in this country is
late in summer or early in the fall. Many also moult again the following
spring, when they put on their wedding dress; and one of the curious
things about this change of plumage is, that the new feathers often come
out quite unlike those that were cast off. So a bird may differ much in
appearance at different seasons and ages--in fact, most birds do. The
male also differs in many cases from the female, being more handsomely
dressed than his mate."
"I don't think that's fair," said Dodo. "I shouldn't like Nat to have
nicer clothes than I wear."
"But it is best for Bird People," replied the Doctor, "that the mother
bird, who has to keep house and tend to the little ones, should not be
too conspicuous. She is best protected from enemies when her colors are
plain, and especially when they match the foliage in which she sits on
her nest. If her mate has only himself to look out for, it does not so
much matter how bright his plumage may be. The colors of some birds are
so exactly like their surroundings, that you might look long before you
could find the sober, quiet female, whose mate is flashing his gay
plumage and singing his finest song, perhaps for the very purpose of
attracting your attention away from his home. 'Protective coloration,'
is what the Wise Men call it."
"What makes all the different colors of birds, Doctor?" asked Rap.
"That is a hard question to answer. It is natural for birds to have
particular colors, just as some people have black eyes and hair, while
others have blue eyes and yellow hair. But I can tell you one thing
about that. Look at this Sparrow. All the colors it shows are _in_ the
feathers, whose various markings are due to certain substances called
'pigments,' which filter into the feathers, and there set in various
patterns. The feathers are painted inside by Nature, and the colors show
through. You see none of these colors are shiny like polished metal. But
I could show you some birds whose plumage glitters with all the hues of
the rainbow. That glittering is called 'iridescence.' It does not
depend upon any pigment in the substance of the feathers, but upon the
way the light strikes them. It is the same with the beautiful tints we
see on a soap-bubble. The film of water itself is colorless, but it
becomes iridescent. You might divide all the colors of birds into two
classes--those that depend upon pigments in the feathers, and those that
depend upon the play of light on the feathers."
"That's pretty hard to remember," said Nat; "but I know how a
soap-bubble looks, though I never saw any birds look that way. Please
show us one."
"I will show you two," answered the Doctor, who then went to his glass
case, and took out a Wild Pigeon and a Hummingbird. "Look at the shining
tints on the neck of this Pigeon, and see how the throat of this
Hummingbird glitters when I turn it to the light."
"That's the prettiest color I ever saw," said Nat, "and I can remember
about it now. But," he added, thinking of the way he had seen hens mope
when they were moulting, "does it hurt birds to lose their feathers,
uncle?"
"It is probably not as comfortable as being nicely dressed, and
sometimes they seem quite miserable, especially if they shed old
feathers faster than new ones can grow to replace the lost ones. Some
birds, like Ducks, lose their wing-feathers all at once, and cannot fly
for quite a while. But Heart of Nature is kind to his children, as a
rule. Most birds shed their rowing feathers one at a time in each wing,
so that they never lose their power of flight. Now this will do for
wings, tails, and feathers. Come! what is the next thing you notice
about this Sparrow? Is it entirely covered with feathers?"
"Of course it isn't," said Dodo; "it hasn't any feathers on its beak or
on its feet, else how could it eat and hop about?"
"That is right. These parts of a Sparrow are bare; they never have any
feathers; and the skin on them is hard and horny, as different from soft
thin skin as finger-nails. Now look at the beak, and think how many
things a Sparrow has to do with it. He has no hands or paws, and so he
must pick up everything he eats with his beak. He has no teeth, and so
he must bite his food with his beak. He feeds on seeds like a Canary
bird; so his beak comes to a sharp point, because seeds are small things
to pick up; and it is very strong and horny, because seeds are hard to
crack, to get at the kernel. Notice, too, children, that his beak is in
two halves, an upper half and a lower half; when these halves are held
apart his mouth is open, so that you can see the tongue inside; and when
the two halves are closed together the mouth is shut. These halves are
called the _upper mandible_ and the _lower mandible_."
"Why, it's just like people's mouths," said Nat, "only people have lips
and teeth."
"Certainly it is like our mouths. Birds are built like ourselves in a
great many things, and live as we do in a great many ways. Bird People
and House People are animals, and all animals must eat to live. A bird's
beak is its mouth, and the under mandible moves up and down, like our
chins when we eat or talk. Birds can talk as well as sing with their
beaks. This Sparrow can say 'Peabody,' and some kinds of Parrots can
repeat whole sentences so as to be understood. That is another thing in
which birds' beaks are like our mouths. Now look again--can you see
anything else about the Sparrow's beak?"
"I see a pair of little holes at the root of the upper mandible," said
Rap.
"Well, those are the nostrils!" said the Doctor. "Birds must breathe,
like ourselves, and when the beak is shut they breathe through the
nostrils."
"So do I," said Dodo; and then she pursed up her pretty red lips
tightly, breathing quite hard through her nose. "I do think," she said,
when she had finished this performance, "birds have faces, with all the
things in them that we have--there are the eyes, too, on each side, like
people's eyes, only they look sideways and not in front. But I don't see
their ears. Have birds any ears, Uncle Roy?"
"I can show you this Sparrow's ears. See here," said the Doctor, who had
run the point of his penknife under a little package of feathers on one
side of the back of the Sparrow's head, and lifted them up; "what does
that look like?"
"It's a hole in the skin that runs into the head," said Nat. "Can birds
hear through that?"
"Of course they can. Ears of all animals are made to hear with. This
Sparrow can hear quite as well as you can, Nat. Now think, children, how
many things we have found about this Sparrow's head that are quite like
our own,--ears, eyes, nose, mouth, and tongue,--only there are no lips
or teeth, because the horny beak, with its hard edges and sharp point,
answers both for lips and teeth. I want you to learn from this how many
things are really alike in Bird People and House People, though they
look so different at first sight. When we come to the bird stories, you
will find that birds differ very much among themselves in all these
things. I will show you all sorts of beaks, of different sizes and
shapes. Here are pictures of several kinds of beaks--see how much they
differ in shape! But they are all beaks, and all beaks are mouths. They
all answer the same purposes in birds' lives, and the purposes are the
same as those of our mouths. But now, what do you notice about this
Sparrow's feet?"
"They are not a bit like my feet," said Dodo; "they are so long and slim
and hard, and the toes stick out so all around. I think mine are nicer."
"But they would not be so useful as this Sparrow's if you had to live in
a bush and hop about on the twigs," said the Doctor. "The bird's feet
are fixed as nicely for that, as yours are for walking on the ground. I
can show you, too, little girl, that a Sparrow's feet are a great deal
more like yours than you think. Come, Rap! Tell me what you see about
this bird's feet."
"Why, they are the ends of its legs, and there is a long slim part
beyond the feathers, hard and horny like the beak, and at the end of
this are four toes, three in front and one behind, and they've all sharp
claws on their ends."
"Very well said, my boy! Now I will show you that such feet as the
Sparrow has are as much like Dodo's as a Sparrow's beak is like her
mouth. Begin with the claws--"
[Illustration: FIG. 1. Insect-eating bill of Robin; 2. Seed-crushing
bill of a Sparrow; 3. Snapping bill of Whip-poor-will; 4. Needle bill of
Hummingbird; 5. Chiselling bill of Woodpecker; 6. Climbing bill of
Paroquet; 7. Tearing bill of Falcon; 8. Grooved drinking bill of Dove;
9. Gleaning bill of Ruffed Grouse; 10. Wedge bill of Plover; 11.
Straight probing bill of Snipe.]
[Illustration: FIG 12: Curved probing bill of Curlew; 13. Spearing bill
of Green Heron; 14. Strainer bill of Duck; 15. Hooked bill of Gull; 16.
Ornamental bill of male Puffin in breeding season.]
"I know!" exclaimed Dodo, "toe-nails! Only I think they need cutting!"
"Of course they are toe-nails," said the Doctor. "Don't nails grow on
the ends of toes? All kinds of claws, on the ends of birds' and other
animals' toes, are the same as nails. Some are long, sharp, and curved,
like a cat's or a Sparrow's, and some are flat and blunt, like ours. I
could show you some birds with claws that look just like our
finger-nails. Toes, too, are pretty much the same; only this Sparrow,
like most other birds, has but four, with three of them in a line in
front, and the other one pointing backward. That is what makes its foot
as good as a hand to hold on with when it perches on slender twigs.
Almost all birds have their toes fixed that way. Some, that do not
perch, have no hind toe; and birds that swim have broad webs stretched
between their front toes, like Ducks. All the different kinds of feet
birds have are fitted for the ways they move about on the ground, or
water, or among the branches of trees and bushes, just as all their
shapes of beaks are fitted for the kind of food they eat and the way
they pick it up. Here are two pictures that will show you several
different kinds of feet. Now you must answer the next question, Nat;
what do toes grow on?"
"Feet!" said Nat promptly, then adding: "But this Sparrow hasn't any
feet except its toes; they grow on its legs, because the rest of the
horny part stands up--I've noticed that in Canaries."
"But all this horny part is the foot, not the leg," answered the Doctor,
"though it does stand up, as you say. How could toes grow from legs
without any feet between? They never do! There has to be a foot in
every animal between the toes and the legs. Now what do you call the end
of your foot which is opposite the end on which the toes grow?"
[Illustration: FIG. 1. Ordinary foot of perching birds; 2. Foot of
Nighthawk, with a comb on claw of middle toe; 3. Climbing foot of
Woodpecker, with two hind toes; 4. Grasping foot of Osprey, for holding
prey.]
[Illustration: FIG. 5. Scratching foot of Ruffed Grouse; 6. Wading foot
of Golden Plover, with only three toes; 7. Wading foot of Snipe, with
short hind toe; 8. Wading foot of Green Heron, with long hind toe; 9.
Swimming foot of Coot, with lobed toes; 10. Swimming foot of Canada
Goose, with three toes webbed; 11. Swimming foot of Cormorant, with all
four toes webbed.]
"It's the heel in people, but I should think the hind toe of a bird was
its heel," said Nat doubtfully, and beginning to think he did not
understand.
"You might think so," said the Doctor; "but you would be wrong. All this
horny part that a bird stands up on is its foot. And the top of it,
nearest to the feathers, is the heel. Don't you see, when I bend the
foot _so_," continued the Doctor, as he bent the Sparrow's foot forward,
"that the top of the horny part makes a joint that stands out backward,
in the same position your heel always has? All this slender horny part
of the foot, above the roots of the toes, corresponds to the instep of
your foot, and of course the heel comes next. You must remember the name
of it--the Wise Men call it the _tarsus_."
"Then hasn't a bird got any legs, Uncle Roy, only just feet?" asked
Dodo.
"Oh! yes; legs too, with a knee-joint and a hip-joint, like ours. But
all these parts are up closer to the body, and hidden by the feathers,
so that you cannot see them."
As the Doctor said this there was a great commotion. Quick, who had been
watching the mouse hole all the while, gave a sharp bark and pounced on
something. There was a feeble squeak, and it was all over with a mouse
which had ventured too far from its hole.
"Poor little mousey!" said the Doctor, as he took the limp body from
the terrier's mouth. "It is quite dead. I am sorry, but it might have
nibbled some of my birds. Besides, this is exactly what I wanted to
teach you something about. Who can tell me the difference between a
mouse and a Sparrow?"
"I can!" said Dodo; "it's all difference; a mouse hasn't any feathers,
or any wings, and it has four feet, and a long tail and whiskers and
teeth--"
"That will do, little girl, for differences; do you see anything alike
between a Sparrow and a mouse, Rap?"
"I think the fur is something like feathers, Doctor," answered Rap; "and
you told us how a beak was like a mouth without any teeth or lips; then
a mouse has four feet and legs; but a bird has only two feet, and two
wings instead of four legs and feet like a mouse."
"That is just what I want you all to think about," said the Doctor. "Now
listen. If a Sparrow has a pair of feet that correspond to a mouse's
hind feet, what do you think a Sparrow's wings correspond to in a
mouse?"
"I should think they would be something like a mouse's fore feet,"
answered Rap, after thinking a moment.
"That is exactly right. Birds and beasts are alike in many respects.
They have heads, necks, and bodies; they have tails; and they have
limbs. Beasts have two pairs of limbs. We call them fore legs and hind
legs. People have two pairs also. We call them arms and legs. So you see
our arms correspond to the fore legs of beasts, though we never use them
for moving about, except when we go on our hands and knees, or climb
trees, or swim in the water. And as for birds--why, their fore limbs
are turned into wings, to fly with, so that they walk or hop on their
hind limbs only, just as we do. Animals that go on all fours are called
_quadrupeds_. Animals that go on their two hind limbs only, like Bird
People and House People, are called _bipeds_. A Sparrow's wings are just
as much like a mouse's fore legs, as a Sparrow's feathers are like a
mouse's fur."
"How funny!" said Dodo. "But how are a bird's wings like fore legs, when
they haven't got any paws or toes--or fingers--or claws--only just long
feathers?"
"They have fingers, and some birds' wings have claws; only you cannot
see them, because they are all wrapped up in the skin and covered over
with the feathers. Some day--not to-day, because you have had a long
lesson already--I will show you a bird's wing with only its bones. Then
you will see that it has finger-bones at the end, then hand-bones next,
then bones that run from the wrist to the elbow, and then one bone that
runs from the elbow to the shoulder--almost the same bones that people
have in their fingers, hands, wrists, and arms. So you see wings are the
same to a bird that fore legs are to a mouse or arms are to us.
"I could go through all the inside parts of birds, and show you
something like the same parts in people,--stomach and bowels, to take
care of the food they eat and turn it into blood to nourish them; lungs
to breathe with, and keep the blood pure; heart to beat and thus pump
the warm blood into all parts of the body; brain and nerves, which are
what birds think and feel with, just as we do with ours; and all their
bones, which together make what we call the _skeleton_, or framework of
the body, to keep the flesh in shape and support the other organs."
"Dear me!" sighed Dodo; "there must be ever so many more things inside
of birds that we can't see, than there are outside."
"Of course there are!" said the Doctor. "It won't be very hard for you
to remember the outside parts, and learn the names of them all. I have
told you most of them that you need to remember, to understand the
stories I am going to tell you about birds. See here! What do you think
of this?"
[Illustration: Outside parts of a bird.]
So saying, the Doctor unrolled a large sheet of drawing-paper that hung
on the wall. "Here is a picture of the White-throated Sparrow, drawn so
big you can see it almost across the room, with all the outside parts of
which you must learn the names. You see the names are all on the
picture, too; I am going to make it smaller, and put it in the book I
will write for you, so you can look at it whenever you wish.
"It is almost dinner-time now, and you must be very hungry. But now I
must tell you one thing more. You know there are so many, many different
kinds of birds and other animals that nobody could remember them unless
they were classified. To classify is to put things that are most alike
closest together, then next nearest them things that are next most
alike, and to keep furthest apart those things that are least alike. Now
it is true that all beasts, birds, snakes, lizards, frogs, and fishes
have some things alike, though each has some other things different from
all the rest. If they were not all alike in some things, we could not
call them all animals. One of the things in which all the animals I have
named are alike is, that they all have skeletons. One of the things in
which all their skeletons are alike is, that they have backbones.
Backbones are the chains of bones that run along the back from the head
to the tail. Backbones are called by the Wise Men _vertebrae_; animals
that have backbones are named _Vertebrates_; and animals that lack
backbones are named _Invertebrates_."
"Tell us the names of some Invertebrates, please, Doctor," said Rap.
"Well, all sorts of insects are Invertebrates, and so are lobsters and
crabs, oysters and clams, worms, starfishes, jelly-fishes, corals, and
even sponges. Then there are some too small to see without a microscope.
But never mind about Invertebrates now. I only want you to remember that
all beasts, birds, reptiles, and fishes are Vertebrates, and that there
are five principal classes of them. If I should tell you as much about
them as I have about the Building of a Bird, you would see that they are
all built on what we call the Vertebrate plan of structure. Here is a
chart of the Classes of Vertebrates--you can study it this afternoon,
till you learn it by heart."
VERTEBRATES
_Animals with Backbones_
CLASS I. Mammals.--Warm-blooded animals which have fur or hair, bring
forth their young alive, and nurse them. House People are Mammals.
CLASS II. Birds.--Warm-blooded animals which have feathers and lay eggs.
CLASS III. Reptiles.--Cold-blooded animals which have scaly skins, like
lizards, snakes, and turtles.
CLASS IV. Batrachians.--Cold-blooded animals which have naked skins,
like frogs, toads, and newts.
All the foregoing classes, except a few of the Batrachians, breathe air
in lungs, and almost all, except snakes, have legs; none now living can
fly, except bats and birds; but bats are Mammals.
CLASS V. Fishes.--Cold-blooded animals which have either scaly or naked
skins, but no fur or feathers; which live in the water, breathe it with
their gills, and swim in it with fins.